Method for fabricating metal-insulator-metal capacitor

ABSTRACT

A method for fabricating a metal-insulator-metal capacitor is described. A first metal layer is formed on a substrate. A plasma treatment is performed on the surface of the first metal layer. Then, a first oxide layer, a nitride layer and a second oxide layer are formed in sequence over the first metal layer. Thereafter, a second metal layer is formed on the second oxide layer. The second metal layer, the second oxide layer, the nitride layer, the first oxide layer and the first metal layer are defined to form the metal-insulator-metal capacitor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating a capacitor.More particularly, the present invention relates to a method forfabricating a metal-insulator-metal capacitor.

2. Description of the Related Art

With great advances in technologies, semiconductor devices have foundincreasing number of applications. A large number of semiconductordevices each having a different function is used inside computers,communication equipment and consumer electronic products. Capacitor isone of the most basic and important semiconductor devices that has anumber of functions including the de-coupling of noise and the storageof electric charges. Among the various types of capacitors, themetal-insulator-metal (MIM) capacitor plays an important role incircuits, particularly in mixed circuits of signal devices and logicdevices.

The conventional method of fabricating a metal-insulator-metal capacitorincludes the following steps. First, a metal layer is formed on asubstrate to serve as the bottom electrode of the capacitor. Then, anoxide/nitride/oxide (ONO) composite layer is formed over the metal layerto serve as a dielectric layer for the capacitor. Thereafter, anothermetal layer is formed over the ONO composite layer to serve as the topelectrode of the capacitor. Finally, the two metal layers and the ONOlayer are defined to form the metal-insulator-metal (MIM) capacitor.

It should be noted that the permissible size of the capacitor continuesto shrink with the development and increasing integration of theintegrated circuits (ICs). Therefore, for an electronic product thatincorporates a capacitor, the capacitor may have insufficientcapacitance per unit area for proper functioning. To resolve thisproblem, the most common method is to reduce the thickness of thedielectric layer of the capacitor so that the capacitance per unit areaof the capacitor is increased.

However, due to the unevenness of the metal layer that serves as thebottom electrode, the foregoing method of reducing the thickness of thedielectric layer above the bottom electrode may lead to lowering of thebreakdown voltage of the capacitor. In some cases, even the reliabilityof the capacitor may be seriously compromised.

SUMMARY OF THE INVENTION

Accordingly, at least one objective of the present invention is toprovide a method for fabricating a metal-insulator-metal (MIM) capacitorcapable of increasing the breakdown voltage and the reliability of theMIM capacitor.

At least another objective of the present invention is to provide analternative method for fabricating a metal-insulator-metal (MIM)capacitor equally capable of increasing the breakdown voltage and thereliability of the MIM capacitor.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a method for fabricating a metal-insulator-metal(MIM) capacitor. First, a first metal layer is formed on a substrate. Afirst plasma treatment is performed on the surface of the first metallayer. Then, a first oxide layer, a nitride layer, a second oxide layerand a second metal layer are sequentially formed over the first metallayer. Thereafter, the second metal layer, the second oxide layer, thenitride layer, the first oxide layer and the first metal layer aredefined to form the metal-insulator-metal (MIM) capacitor.

According to one embodiment of the present invention, the reactive gasused in the first plasma treatment includes an inert gas, nitrogen or anoxygen-containing gas, for example. The oxygen-containing gas includesoxygen or nitrous oxide, for example. In one embodiment, if the reactivegas used in the first plasma treatment is an oxygen-containing gas, athird oxide layer is formed on the first metal layer after performingthe first plasma treatment.

According to one embodiment of the present invention, the first plasmatreatment can be carried out in-situ. In another embodiment, the firstplasma treatment can be carried out ex-situ.

According to one embodiment of the present invention, after forming thenitride layer but before forming the second oxide layer, the methodfurther includes performing a second plasma treatment on the surface ofthe nitride layer. The reactive gas used in the second plasma treatmentincludes an oxygen-containing gas, for example. The oxygen-containinggas is oxygen or nitrous oxide, for example. Furthermore, afterperforming the second plasma treatment, a third oxide layer is formedover the nitride layer. In addition, the second plasma treatment can becarried out in situ. In another embodiment, the second plasma treatmentcan be carried out in ex-situ.

According to one embodiment of the present invention, the first metallayer and the second metal layer are made of aluminum, copper,palladium, ruthenium, titanium nitride or tantalum nitride, for example.

According to one embodiment of the present invention, the first metallayer and the second metal layer are formed, for example, by performinga direct current (DC) magnetic-sputtering process, a chemical vapordeposition (CVD) process or an evaporation process.

According to one embodiment of the present invention, the second oxidelayer, the nitride layer and the first oxide layer are formed byperforming a chemical vapor deposition process, for example.

The present invention also provides an alternative method forfabricating a metal-insulator-metal (MIM) capacitor. First, a firstmetal layer is formed on a substrate. Then, a first oxide layer and anitride layer are sequentially formed over the first metal layer.Thereafter, a plasma treatment is performed on the surface of thenitride layer. Afterwards, a second oxide layer and a second metal layerare sequentially formed over the nitride layer. Thereafter, the secondmetal layer, the second oxide layer, the nitride layer, the first oxidelayer and the first metal layer are defined to form themetal-insulator-metal (MIM) capacitor.

According to one embodiment of the present invention, after performingthe plasma treatment, the method further includes forming a third oxidelayer on the surface of the nitride layer.

According to one embodiment of the present invention, the reactive gasuse din the plasma treatment includes an oxygen-containing gas, forexample. The oxygen-containing gas includes oxygen or nitrous oxide, forexample.

According to one embodiment of the present invention, the plasmatreatment can be carried out in situ, for example. In anotherembodiment, the plasma treatment can be carried out in ex-situ.

According to one embodiment of the present invention, the first metallayer and the second metal layer can be made of aluminum, copper,palladium, ruthenium, titanium nitride or tantalum nitride, for example.

According to one embodiment of the present invention, the first metallayer and the second metal layer are formed, for example, by performinga DC magnetic-sputtering process, a chemical vapor deposition process oran evaporation process.

According to one embodiment of the present invention, the second oxidelayer, the nitride layer and the first oxide layer are formed byperforming a chemical vapor deposition process, for example.

In the present invention, a plasma treatment is performed to the surfaceof a first metal layer so that the surface of the metal layer isplanarized. Thus, the breakdown voltage is increased and the reliabilityof the capacitor is enhanced, and the prior problem of having a lowbreakdown voltage in the capacitor is alleviated. Furthermore, themethod can also include performing a plasma treatment on the surface ofthe nitride layer or on the surface of both the first metal layer andthe nitride layer, for increasing the breakdown voltage and improvingthe reliability of the capacitor.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIGS. 1A through 1G are schematic cross-sectional views showing thesteps for fabricating a metal-insulator-metal capacitor according to oneembodiment of the present invention.

FIGS. 2A through 2E are schematic cross-sectional views showing thesteps for fabricating a metal-insulator-metal capacitor according toanother embodiment of the present invention.

FIG. 3 is a graph showing the relationships of the leakage currentversus the voltage for a metal-insulator-metal capacitor fabricated bythe conventional method and by the method according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIGS. 1A through 1G are schematic cross-sectional views showing thesteps for fabricating a metal-insulator-metal capacitor according to oneembodiment of the present invention. As shown in FIG. 1A, a substrate100 is provided. The substrate 100 is a silicon substrate or a substratehaving semiconductor devices or metallic interconnect structures alreadyformed thereon, for example. Then, a metal layer 102 is formed over thesubstrate 100 to serve as the bottom electrode of ametal-insulator-metal (MIM) capacitor. The metal layer 102 is fabricatedusing aluminum, copper, palladium, ruthenium, titanium nitride ortantalum nitride, for example. The method of forming the metal layer 102includes, for example, performing a DC magnetic-sputtering process, achemical vapor deposition process or an evaporation process.

As shown in FIG. 1B, a plasma treatment 104 is performed on the surfaceof the metal layer 102. The plasma treatment 104 can be carried out insitu, for example. In other words, the process of fabricating the metallayer 102 and the plasma treatment on the surface of the metal layer 102can be carried out in the same reaction chamber or the same processingmachine. Alternatively, the plasma treatment 104 can be carried out inex-situ. Furthermore, the reactive gas used in the plasma treatment 104includes an inert gas, nitrogen or an oxygen-containing gas, forexample. The oxygen-containing gas includes oxygen or nitrous oxide, forexample.

It should be noted that the plasma treatment 104 can planarize thesurface of the metal layer 102 and prevent the prior low breakdownvoltage problem in the conventional capacitor when inert gas or nitrogenis used as a reactive gas in the plasma treatment 104. Hence, both thebreakdown voltage and the reliability of the capacitor are increased. Onthe other hand, if an oxygen-containing gas is used as a reactive gas inthe plasma treatment 104, an oxide layer 106 is formed on the metallayer 102 as shown in FIG. 1C. Similarly, both the breakdown voltage andthe reliability of the capacitor are increased.

As shown in FIG. 1D, an oxide layer 108 is formed over the oxide layer106. The oxide layer 108 is a silicon oxide layer formed, for example,by performing a chemical vapor deposition process. The chemical vapordeposition process includes a plasma-enhanced chemical vapor deposition(PECVD) process, for example. Thereafter, a nitride layer 110 is formedover the oxide layer 108. The nitride layer 110 is a silicon nitridelayer formed, for example, by performing a chemical vapor depositionprocess. The chemical vapor deposition process includes aplasma-enhanced chemical vapor deposition (PECVD) process, for example.

In one embodiment of the present invention, after forming the nitridelayer 110 but before forming the oxide layer, a plasma treatment 112 canbe carried out on the surface of the nitride layer 110. The plasmatreatment is performed using a reactive gas such as an oxygen-containinggas. The oxygen-containing gas is oxygen or nitrous oxide, for example.The foregoing plasma treatment process 112 will form an oxide layer 114over the nitride layer 110 as shown in FIG. 1E. Similarly, the plasmatreatment 112 can increase the breakdown voltage and improve thereliability of the capacitor. Furthermore, the plasma treatment 112 canbe carried out in-situ, for example. However, the plasma treatment 112can be carried out in ex-situ.

As show in FIG. 1F, another oxide layer 116 is formed over the oxidelayer 114. The oxide layer 116 is a silicon oxide layer formed, forexample, by performing a chemical vapor deposition process. The chemicalvapor deposition process includes a plasma-enhanced chemical vapordeposition (PECVD) process, for example. Then, a metal layer 118 isformed over the oxide layer 116 to serve as the top electrode of themetal-insulator-metal capacitor. The metal layer 118 is fabricated usingaluminum, copper, palladium, ruthenium, titanium nitride or tantalumnitride, for example. The method of forming the metal layer 118includes, for example, performing a DC magnetic-sputtering process, achemical vapor deposition process or an evaporation process.

As shown in FIG. 1G, the metal layer 118, the oxide layer 116, the oxidelayer 114, the nitride layer 110, the oxide layer 108, the oxide layer106 are defined to form a metal-insulator-metal (MIM) capacitor 120. Theprocess of defining the foregoing layers includes performing aphotolithographic and etching process, for example.

FIGS. 2A through 2E are schematic cross-sectional views showing thesteps for fabricating a metal-insulator-metal capacitor according toanother embodiment of the present invention. As shown in FIG. 2A, asubstrate 200 is provided. Then, a metal layer 202 is formed over thesubstrate 200 to serve as the bottom electrode of ametal-insulator-metal (MIM) capacitor. The metal layer 202 is fabricatedusing aluminum, copper, palladium, ruthenium, titanium nitride ortantalum nitride, for example. The method of forming the metal layer 202includes, for example, performing a DC magnetic-sputtering process, achemical vapor deposition process or an evaporation process.

Then, an oxide layer 204 is formed over the metal layer 202. The oxidelayer 204 can be a silicon oxide layer formed, for example, byperforming a chemical vapor deposition process. The chemical vapordeposition process includes a plasma-enhanced chemical vapor deposition(PECVD) process, for example. Thereafter, a nitride layer 206 is formedover the oxide layer 204. The nitride layer 206 can be a silicon nitridelayer formed, for example, by performing a chemical vapor depositionprocess. Similarly, the chemical vapor deposition process includes aplasma-enhanced chemical vapor deposition (PECVD) process, for example.

As shown in FIG. 2B, a plasma treatment 208 is performed on the surfaceof 1o the nitride layer 206. The reactive gas used in plasma treatment208 includes an oxygen-containing gas. The oxygen-containing gas isoxygen or nitrous oxide, for example. Furthermore, the plasma treatmentprocess 112 can be carried out in situ or ex-situ, for example. Morespecifically, the plasma treatment 208 forms an oxide layer 210 on thenitride layer 206 as shown in FIG. 2C. The oxide layer 210 serves toincrease the breakdown voltage and improve the reliability of thecapacitor.

As shown in FIG. 2D, another oxide layer 212 is formed over the oxidelayer 210. The oxide layer 212 can be a silicon oxide layer formed, forexample, by performing a chemical vapor deposition process. The chemicalvapor deposition process includes a plasma-enhanced chemical vapordeposition (PECVD) process, for example. Then, a metal layer 214 isformed on the oxide layer 212 to serve as the top electrode of themetal-insulator-metal (MIM) capacitor. The metal layer 214 is fabricatedusing aluminum, copper, palladium, ruthenium, titanium nitride ortantalum nitride, for example. The method of forming the metal layer 214includes, for example, performing a DC magnetic-sputtering process, achemical vapor deposition process or an evaporation process.

As shown in FIG. 2E, the metal layer 214, the oxide layer 212, the oxidelayer 210, the nitride layer 206, the oxide layer 204 and the metallayer 202 are defined to form the metal-insulator-metal capacitor 216.The method of defining the foregoing layers includes performing aphotolithographic and etching process, for example.

FIG. 3 is a graph showing the relationships of the leakage currentversus voltage (I-V) characteristic between a MIM capacitor fabricatedby the conventional method and a MIM capacitor fabricated by the methodaccording to the present invention. lo As shown in FIG. 3, the Y-axisrepresents the leakage current (Ig) and the X-axis represents the DCvoltage Vg acting on the metal layer. The curve C1 shows the I-Vcharacteristic of a conventional metal-insulator-metal capacitor and thecurve C2 shows the I-V characteristic of the metal-insulator-metalcapacitor fabricated according to the method in the present invention.As shown in FIG. 3, under a constant operating voltage, the MIMcapacitor fabricated according to the present invention has a smallerleakage current compared to the conventional MIM capacitor. In otherwords, the MIM capacitor fabricated using the method according to thepresent invention has a higher breakdown voltage and a higher degree ofreliability.

In summary, the plasma treatment process performed to the metal layerand/or the nitride layer according to the method in the presentinvention can produce an oxide layer thereon or planarize the surface ofthe metal layer. Therefore, the problem of having a lower breakdownvoltage in the conventional capacitor can be alleviated. Ultimately, thecapacitor can have a higher breakdown voltage and better reliability.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1-15. (canceled)
 16. A method for fabricating a metal-insulator-metalcapacitor, comprising the steps of: forming a first metal layer on asubstrate; forming a first oxide layer over the first metal layer;forming a nitride layer over the first oxide layer; performing a plasmatreatment on the surface of the nitride layer; forming a second oxidelayer over the nitride layer; forming a second metal layer over thesecond oxide layer; and defining the second metal layer, the secondoxide layer, the nitride layer, the first oxide layer and the firstmetal layer to form the metal-insulator-metal capacitor.
 17. The methodfor fabricating the metal-insulator-metal capacitor of claim 16, whereinafter performing the plasma treatment, the method further includesforming a third oxide layer over the surface of the nitride layer. 18.The method for fabricating the metal-insulator-metal capacitor of claim16, wherein a reactive gas used in the plasma treatment includes anoxygen-containing gas.
 19. The method for fabricating themetal-insulator-metal capacitor of claim 18, wherein theoxygen-containing gas includes oxygen or nitrous oxide.
 20. The methodfor fabricating the metal-insulator-metal capacitor of claim 16, whereinthe plasma treatment is performed in-situ.
 21. The method forfabricating the metal-insulator-metal capacitor of claim 16, wherein theplasma treatment is performed ex-situ.
 22. The method for fabricatingthe metal-insulator-metal capacitor of claim 16, wherein the first metallayer and the second metal layer are made of aluminum, copper,palladium, ruthenium, titanium nitride or tantalum nitride.
 23. Themethod for fabricating the metal-insulator-metal capacitor of claim 16,wherein the step for forming the first metal layer and the second metallayer includes performing a DC magnetic-sputtering process, a chemicalvapor deposition process or an evaporation process.
 24. The method forfabricating the metal-insulator-metal capacitor of claim 16, wherein thestep for forming the second oxide layer, the nitride layer and the firstoxide layer includes performing a chemical vapor deposition process.